Methods for securing spinal rods

ABSTRACT

A method of securing a spinal rod to a spine includes providing a head portion having a channel extending therethrough for receiving a spinal rod, the channel and the head portion being bounded by a first side wall and a second side wall. The method includes providing a bone fastener depending from the head portion, arranging the spinal rod in the channel of the head portion, and providing a locking cap having first and second portions that are rotatable relative to one another, the second portion of the locking cap having an underside with a recess. The method includes assembling the locking cap with the head portion so that the first portion is between the first and second side walls and so that the recess of the second portion of the locking cap is in contact with the spinal rod. While maintaining the recess of the second portion of the locking cap in contact with the spinal rod, the first portion of the locking cap is rotated, such rotation translating into a locking force applied by the second portion of the locking cap onto the spinal rod.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject application is a continuation of U.S. application Ser. No.10/365,182, filed Feb. 12, 2003, which is a continuation of U.S.application Ser. No. 09/487,942, filed Jan. 19, 2000, now U.S. Pat. No.6,565,565, which is a continuation-in-part of both U.S. application Ser.No. 09/167,439, filed Oct. 6, 1998, now abandoned, and U.S. applicationSer. No. 09/098,927, filed Jun. 17, 1998, now U.S. Pat. No. 6,090,111,the disclosures of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject disclosure relates to implantable spinal stabilizationsystems for surgical treatment of spinal disorders, and moreparticularly, to a device for connecting cylindrical spinal rods of aspinal stabilization system to the spine.

2. Background of the Related Art

The spinal column is a complex system of bones and connective tissuethat protects critical elements of the nervous system. Despite thesecomplexities, the spine is a highly flexible structure, capable of ahigh degree of curvature and twist through a wide range of motion.Trauma or developmental irregularities can result in spinal pathologiesthat limit this range of motion.

For many years, orthopedic surgeons have attempted to correct spinalirregularities and restore stability to traumatized areas of the spinethrough immobilization. Over the past ten years, spinal implant systemshave been developed to achieve immobilization. Examples of such systemsare disclosed in U.S. Pat. Nos. 5,102,412 and 5,181,917 to Rogozinski.Such systems often include spinal instrumentation having connectivestructures such as elongated rods, which are placed on opposite sides ofthe portion of the spinal column intended to be immobilized. Screws andhooks are commonly utilized to facilitate segmental attachment of suchconnective structures to the posterior surfaces of the spinal laminae,through the pedicles, and into the vertebral bodies. These componentsprovide the necessary stability both in tension and compression toachieve immobilization.

Various fastening mechanisms have been provided in the prior art tofacilitate securement of screws and hooks to the connective structuresof a spinal stabilization system. For example, U.S. Pat. No. 5,257,993to Asher discloses an apparatus for use in retaining a spinal hook on anelongated spinal rod. The apparatus includes a body extending upwardlyfrom a hook portion and having an open-ended recess for receiving aspinal rod and an end cap engageable with the body to close the recess.A set screw is disposed in the center of the end cap to clamp the rod inthe recess of the body. The end cap and body are interconnectable bydifferent types of connectors including a bayonet connector, a linearcam connector or a threaded connector. Other examples of fasteningmechanism for facilitating attachment of screws and hooks to theconnective structures of a spinal stabilization system are disclosed inU.S. Pat. No. 5,437,669 to Yuan et al. and U.S. Pat. No. 5,437,670 toSherman et al.

In each of these prior art examples, threaded fasteners are used tofacilitate securement of the connector to the spinal rod. Yet it is wellknown that threaded fasteners can become loosened under the influence ofcyclically applied loads commonly encountered by the spinal column.Furthermore, during assembly, excessive torque applied to a threadedfastener can cause damage to the fastener as well as to the connectivedevice with which it is associated.

It would be beneficial to provide a more reliable and effectivemechanism for facilitating the attachment of screws, hooks and clamps tothe connective structures of a spinal stabilization system.

SUMMARY OF THE DISCLOSURE

The subject disclosure is directed to a device for securing a spinal rodto a fixation device such as a pedicle screw or a lamina hook. Thedevice disclosed herein includes a head portion configured to receive aspinal rod, a locking cap configured to engage the head portion and thespinal rod upon rotation of the locking cap relative to the head portionto secure the position of the head portion relative to the spinal rod,and a fastener portion extending from the head portion and configured toengage the spine. The fastener portion of the device can be in the formof a screw, hook or clamp, or any other configuration known in the art.

The head portion of the device has a channel extending therethrough forreceiving a spinal rod and the channel is preferably bounded by opposedside walls each having an arcuate engagement slot defined therein. Thelocking cap preferably has opposed arcuate engagement flanges configuredfor reception in the opposed arcuate engagement slots of the headportion upon rotation of the locking cap relative to the head portion.Preferably, the opposed engagement slots are each defined in part byinclined slot surfaces, with the angle of the inclined surface of oneengagement slot being opposite that of the opposed engagement slot.Similarly, the opposed engagement flanges are preferably each defined inpart by inclined flange surfaces, with the angle of the inclined surfaceof one engagement flange being opposite that of the opposed engagementflange. The head portion also preferably includes structure forinteracting with the locking cap to prevent the opposed side walls ofthe head portion from expanding radially outwardly when the arcuateflanges are engaged in the arcuate slots.

Preferably, the locking cap of the device is configured for rotationbetween an initial position in which the arcuate engagement flanges are90° out of phase with the arcuate engagement slots, an intermediateposition in which the arcuate engagement flanges are 45° out of phasewith the arcuate engagement slots, and a locked position in which thearcuate engagement flanges are in phase and intimately engaged with thearcuate engagement slots.

In this regard, the bottom surface of the locking cap preferablyincludes a first recess oriented to accommodate a spinal rod when thelocking cap is in an initial unlocked position, a second recesses whichintersects the first recess at a first angle to accommodate a spinal rodwhen the locking cap is in an intermediate position, and a third recesswhich intersects the elongate recess at a second angle to accommodate aspinal rod when the locking cap is in a final locked position. Inaccordance with a preferred embodiment of the subject disclosure, thefirst recess is an elongate recess, the second recess is a transverserecess, which intersects the elongate recess at a 45° angle, and thethird recess is an orthogonal recess, which intersects the elongaterecess at a 90° angle.

The subject disclosure is also directed to a device for securing aspinal rod to the spine which comprises a head portion having a channelextending therethrough configured to receive a spinal rod, a locking capincluding a first portion configured to engage an interior surface ofthe head portion and a second portion configured to engage an exteriorsurface of a spinal rod received by the channel to secure the positionof the head portion relative to the spinal rod, and a fastener portiondepending from the head portion and configured to engage the spine.

Preferably, the locking cap is a two-piece structure which includes anupper portion configured to engage an interior surface of the headportion and a lower portion configured to engage an exterior surface ofthe spinal rod to secure the position of the head portion relative tothe spinal rod upon rotation of the upper portion relative to the lowerportion and the head portion. The upper portion of the locking capincludes a bottom surface having an axial reception bore defined thereinand the lower portion of the locking cap includes an upper surfacehaving an axial post extending therefrom configured to engage the axialreception bore in the bottom surface of the upper portion of the lockingcap and facilitate the relative rotation of the two parts. The upperportion further includes opposed arcuate engagement flanges configuredfor cammed engagement in correspondingly configured opposed arcuateengagement slots formed in the opposed side walls of the head portionupon rotation of the upper portion relative to the lower portion. Thelower portion further includes a bottom surface having an elongatedhemi-cylindrical recess that is oriented to accommodate a spinal rodextending through the channel in the head portion.

In accordance with one aspect of the subject disclosure, the fastenerportion is formed monolithic with the head portion. In accordance withanother aspect of the subject disclosure, the fastener portion ismounted for movement relative to the head portion. In this regard, thehead portion defines a central axis oriented perpendicular to the spinalrod channel and the fastener portion is mounted for angular movementrelative to the central axis of the head portion. More particularly, thefastener portion includes a generally spherical head and a threadedbody, which depends from the spherical head, and the head portiondefines a seat to accommodate the spherical head and an aperture toaccommodate the threaded body. In use, upon rotation of the upperportion of the locking cap relative to the lower portion of the lockingcap into a locked position, the position of the head portion relative tothe spinal rod and the position of the fastener relative to the headportion become fixed.

These and other unique features of the device disclosed herein and themethod of installing the same will become more readily apparent from thefollowing description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the disclosedapparatus appertains will more readily understand how to construct anduse the same, reference may be had to the drawings wherein:

FIG. 1 is a perspective view of an elongated spinal rod of a spinalstabilization system having attached thereto a bone screw and a bonehook constructed in accordance with a first embodiment of the subjectdisclosure;

FIG. 2 is a perspective view of a locking cap which forms part of thebone screw and bone hook illustrated in FIG. 1, oriented in an invertedposition for ease of illustration;

FIG. 3 is a perspective view of the bone screw and locking cap of FIG. 1separated from one another for ease of illustration;

FIG. 4 is a cross-sectional view of the bone screw of the subjectdisclosure taken along line 4-4 of FIG. 1;

FIG. 5 is a cross-sectional view of the locking cap taken along line 5-5of FIG. 3;

FIGS. 6A through 6D illustrate operative steps associated with attachingthe bone fastener of the subject disclosure to a spinal rod wherein:

FIG. 6A illustrates the step of positioning the spinal rod and lockingcap in the reception channel of the head portion of a fastening deviceof the subject disclosure;

FIG. 6B illustrates the initial orientation of the locking cap relativeto the head portion of a fastening device of the subject disclosurewherein the locking cap is in an unlocked position;

FIG. 6C illustrates the rotation of the locking cap relative to the headportion of a fastening device of the subject disclosure to a partiallylocked position; and

FIG. 6D illustrates the rotation of the locking cap relative to the headportion of a fastening device of the subject disclosure to a lockedposition;

FIG. 7 is a perspective view of a fastening device constructed inaccordance with a second embodiment of the subject disclosure;

FIG. 8 is a perspective view of the fastening device of FIG. 7 with thelocking cap separated for ease of illustration;

FIG. 9 is a perspective view of the locking cap of the fastener deviceof FIG. 7, oriented in an inverted position for ease of illustration;

FIG. 10 is a cross-sectional view of the fastening device of FIG. 7taken along line 10-10 of FIG. 7;

FIG. 11 is a perspective view of an elongated spinal rod of a spinalstabilization system having attached thereto another version of a bonescrew and another version of a bone hook constructed in accordance withanother embodiment of the subject disclosure;

FIG. 12A is an exploded perspective view of the bone screw of FIG. 11with parts separated for ease of illustration including the two-piecelocking cap and multi-axial fastener portion associated therewith;

FIG. 12B is a perspective view, looking upward from below, of thetwo-piece locking cap of the subject disclosure illustrating the bottomsurface features of the component parts thereof:

FIG. 13 is a cross-sectional view of the bone screw of FIG. 11 takenalong line 13-13 of FIG. 11 with the two-piece locking cap in a lockedposition;

FIGS. 14A through 14C illustrate, in counter-clockwise progression, theoperative steps associated with attaching the bone screw of FIG. 11 to aspinal rod by employing the two-piece locking cap of the subjectdisclosure, wherein:

FIG. 14A illustrates the step of positioning the locking cap within thehead portion of the bone screw;

FIG. 14B illustrates the initial unlocked orientation of the upperportion of the locking cap within the head portion of the bone screw;and

FIG. 14C illustrates the step of rotating the upper portion of thelocking cap relative to the lower portion of the locking cap and thehead portion of the bone screw into a locked position to secure theposition of the bone screw with respect to the spinal rod;

FIG. 15 is an exploded perspective view of the bone hook of FIG. 11 withparts separated for ease of illustration including the two-piece lockingcap associated therewith; and

FIG. 16 is a cross-sectional view of the bone hook of FIG. 11 takenalong line 16-16 of FIG. 11 with the two-piece locking cap in a lockedpositions.

These and other features of the apparatus disclosed herein will becomemore readily apparent to those having ordinary skill in the art from thefollowing detailed description of the preferred embodiments taken inconjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals identifysimilar structural elements of the subject apparatus, there isillustrated in FIG. 1 a section of a spinal stabilization systemconstructed in accordance with a preferred embodiment of the subjectdisclosure and designated generally by reference numeral 10.

Referring to FIG. 1, spinal stabilization system 10 includes anelongated spinal rod 12 having a circular cross-section and asubstantially smooth outer surface finish. As illustrated, fasteningdevices in the form of a bone screw 14 and right-angle hook 16 areprovided for securing spinal rod 12 to the spine during a spinalstabilization procedure. Both fastening devices employ a noveltop-loaded locking cap, designated generally by reference numeral 20,which will be described in greater detail hereinbelow with reference toFIG. 2. The novel locking cap achieves significant clinical advantagesover the prior art through its reliability and the ease in which it isinstalled during a spinal stabilization procedure.

It should be recognized that the subject disclosure is not limited inany way to the illustrated bone screw and right-angle hook. Rather,these particular fasteners are merely examples of the type of devicesthat can employ the novel locking cap disclosed herein. Other fastenerscommonly utilized in spinal stabilization systems, such as, for example,hooks having alternative angular geometries as well as clamps are alsoenvisioned. Indeed, it is envisioned that any component designed forattachment to an elongated spinal rod or transverse coupling rod, mayincorporate the novel locking cap of the subject disclosure. Also, anynumber of fastening devices can be applied along the length of thespinal rod.

With continuing reference to FIG. 1. bone screw 14 includes a headportion 22 defining a horizontal axis and a vertical axis. A shankportion 24 depends from the head portion and a threaded portion 26having a helical thread extending about the outer periphery depends fromthe shank portion. The helical thread is particularly adapted tosecurely engage the vertebral bodies of the spine. A channel 28 extendsthrough the head portion 22 along the horizontal axis thereof forreceiving elongated spinal rod 12. As best seen in FIG. 3, channel 28 isdefined by the interior surfaces of side walls 30 and 32 and the curvedlower surface 29, which extends therebetween. Locking cap 20 isdimensioned and configured for reception and engagement in lockingchannel 28 to secure the position of bone screw 14 with respect tospinal rod 12 during a spinal stabilization procedure.

Referring again to FIG. 1, right-angle hook 16 includes a head portion42 defining a horizontal axis and a vertical axis. A hook portion 46depends from the head portion 42 for securement to a vertebral body ofthe spine. A channel 48 extends through the head portion 42 along thehorizontal axis thereof for receiving elongated spinal rod 12. Channel48 is defined by the interior surfaces of opposed side walls 50 and 52and a curved lower surface extending therebetween. Locking cap 20 isdimensioned and configured for reception and engagement in channel 48 tosecure the position of hook 16 with respect to spinal rod 12 during aspinal stabilization procedure.

Referring now to FIG. 2, there is illustrated locking cap 20 in aninverted position to best illustrate structural aspects thereof Lockingcap 20 includes a cylindrical head 62 and a flanged portion 64. Thebottom surface 66 of flanged portion 64 includes an elongate recess 68having a curvature complementary to spinal rod 12 for accommodating thespinal rod when locking cap 20 is in an unlocked position, shown forexample in FIG. 6B. In such a position, the fastening device may bemoved freely along or rotated about the longitudinal axis of the spinalrod. Bottom surface 66 also includes a bifurcated orthogonal recess 70which intersects the elongate recess at a 90° angle and has a curvaturecomplementary to spinal rod 12 to accommodate the spinal rod whenlocking cap 20 is in a locked position, shown for example in FIG. 6D andFIG. 4. In addition, bottom surface 66 includes bifurcated first andsecond transverse recesses 72 and 74 which intersect the elongate recess68 at opposite angles of intersection and have curvatures which arecomplementary to spinal rod 12 to accommodate the spinal rod when thelocking cap 20 is in either of two intermediate positions, one of whichis shown for example in FIG. 6C. In such a position, the fasteningdevice retains the spinal rod but is not fully secured, and if desiredby the surgeon, locking cap 20 can be rotated from the intermediateposition and the fastener moved to an alternative location on the spinalrod. Preferably, the transverse recesses intersect the elongate recessat opposed 45° angles. However, those skilled in the art will readilyappreciate that the transverse recess can be oriented at alternativeintersecting angles. It is also contemplated that the bottom surface canbe flat without any recesses.

Referring to FIGS. 3 and 5, the cylindrical head 62 of locking cap 20includes a hexagonal axial bore 80 extending partially therethrough forreceiving a working implement such as a wrench to facilitate rotation ofthe locking cap 20 relative to the head portion 22 of the fasteningdevice about the vertical axis defined thereby. It envisioned thatalternative tooling configurations known in the art can also be utilizedto facilitate axial rotation of locking cap 20 during a surgicalprocedure. Curved notches 76 and 78 are formed in the inner surfaces ofopposed walls 30 and 32 for accommodating the cylindrical head 62 oflocking cap 20 when the locking cap is received and rotated withinchannel 28.

The flanged portion 64 of locking cap 20 is defined in part by twodiametrically opposed arcuate engagement flanges 82 and 84 which aredimensioned and configured for operative engagement with twocomplementary diametrically opposed arcuate engagement slots 86 and 88defined in the interior surfaces of the opposed side walls 30 and 32 ofhead portion 22. (See FIG. 4).

With continuing reference to FIGS. 3 through 5, engagement flanges 82and 84 define ramped camming surfaces 92 and 94, respectively. Cammingsurfaces 92 and 94 are of opposite angular inclination with respect toone another. More particularly, each engagement flange has a low side(e.g., 82 a of flange 82) and a high side (e.g., 82 b of flange 82),whereby the low sides of the two flanges are diametrically opposed fromone another as are the high sides. Actually, the camming surfaces of theflanges are mirror images of one another. Thus, the locking cap can beinitially oriented with either flange aligned to engage either slot.This versatility adds to the ease in which the locking cap is installedduring a surgical procedure.

As best seen in FIG. 4, the arcuate engagement slots 86 and 88 in headportion 22 of fastener 14 have inclined surfaces that mate with theramped camming surfaces 92 and 94 of flanges 82 and 84. As best seen inFIG. 5, the ramped camming surfaces 92 and 94 are tapered radiallyinwardly to enhance the interlock with the mating surfaces of arcuateengagement slots 86 and 88, which are also tapered to complement theradially inward taper of camming surfaces 92 and 94. This interlockingrelationship serves to prevent the opposed side walls 30 and 32 of headportion 22 from spreading radially outward as the arcuate flanges areengaged with the arcuate slots when the locking cap 20 is rotated to alocked position.

FIGS. 6A through 6D illustrate the steps in securing the fasteningdevice to the spinal rod during a surgical procedure. Althoughattachment of a bone screw 14 is shown, it should be understood, asnoted above, that other fastening devices, e.g., bone hooks, can besecured to the spinal rod 12 using the locking cap and head portionstructure of the present disclosure. Initially, as illustrated in FIG.6A, spinal rod 12 is moved into approximation with the horizontalchannel 28 of head portion 22 such that the periphery of the spinal rod12 is in registration with the curved surface 29 of the channel 28.Locking cap 20 is then top loaded into the channel along the verticalaxis of the fastener in the direction of arrow a. At such a time, spinalrod 12 is accommodated within the elongate recess 68 defined in thebottom surface 66 of locking cap 20 and the bone screw 14 may be movedfreely relative to the spinal rod. The opposed flanged sections 82 and84 of locking cap 20 are 900 out of phase from the opposed arcuateengagement slots 86 and 88 defined in head portion 22, as shown forexample in FIG. 6B.

Thereafter, as shown in FIG. 6C, locking cap 20 is rotated 45° relativeto head portion 22 about the vertical axis thereof. At such a time,spinal rod 12 is accommodated within one of the two transverse recesses72 or 74, depending upon the initial orientation of the locking cap 20with respect to the head portion. Thereupon, the opposed arcuateengagement flanges 82 and 84 of locking cap 20 are only partiallyengaged with the opposed arcuate engagement slots 86 and 88 defined inhead portion 22, as they are 45° out of phase with the slots.Consequently, the locking cap holds the fastener 22 and spinal rod 12together, but does not lock the fastener. In this position, the lockingcap 20 can be readily rotated in the opposite direction to disengagefrom the spinal rod 12 to adjust the position of the bone screw 14 withrespect to the spinal rod 12.

Once the desired position and orientation of the bone screw 14 has beenattained, locking cap 20 is rotated another 90° to the locked positionillustrated in FIG. 6D. At such a time, spinal, rod 12 is accommodatedwithin the orthogonal recess 70 defined in the bottom surface of lockingcap 20. Thereupon, the opposed engagement flanges 82 and 84 of flangedportion 64 are fully engaged with the opposed engagement slots 86 and 88of head portion 22 and the longitudinal and angular orientations of thebone screw 14 are fixed with respect to spinal rod 12, as illustrated inFIG. 4. It should be readily apparent that the manner and method bywhich bone screw 14 hook is attached to spinal rod 12 is identical tothe manner and method by which hook 16 or other fasteners are attachedto spinal rod 12.

Since the rotational range of locking cap 20 is limited, i.e., thelocking cap can only be rotated 90°, it will be readily appreciated thatthe cap cannot be over-torqued. Thus, the damage often caused byover-tightening a conventional threaded locking mechanism, such as a setscrew, is avoided. Furthermore, since the locking cap of the subjectdisclosure has a predetermined locked position, it is unlikely that itwill be under-torqued or left in a loose condition after installation asis common with threaded set screws found in the prior art. That is, byhaving a predetermined locked position, uniform locking forces areprovided for all of the fastening devices used to secure the spinal rod12 along its length and cross threading is reduced.

Referring now to FIGS. 7 and 8, there is illustrated another fasteningdevice constructed in accordance with a preferred embodiment of thesubject disclosure and designated generally by reference numeral 110.Fastening device 110 is similar to fastening devices 12 and 14 in thatit is particularly designed to facilitate securement of a spinal rod tothe spine in a convenient manner. Fastening device 110 includes a headportion 122 having opposed side walls 130 and 132, which define ahorizontal channel 128 in conjunction with the curved lower surface 129extending therebetween. Arcuate tabs 176 and 178 project upwardly fromside walls 130 and 132, respectively, for interacting with locking cap,120.

Referring to FIG. 9, locking cap 120, which is shown in an invertedposition for ease of illustration, includes a hexagonal head 162 acylindrical body 163 and a flanged portion 164. The hexagonal head 162is adapted and configured for interaction with a wrench or similar workimplement. An annular channel 165 extends into the bottom surface ofhexagonal head 162 for receiving arcuate tabs 176 and 168 This positiveinteraction serves to prevent the opposed side walls 130 and 132 of headportion 122 from spreading radially outwardly when arcuate flanges 182and 184 of locking cap 120 are engaged in arcuate slots 186 and 188 ofhead portion 122 upon rotation of locking cap 20 into a locked position.Thus, in this embodiment, the ramped camming surfaces 192 and 194 of thearcuate engagement flanges 182 and 184 need not be provided withradially inwardly directed tapers as provided on flanges 82 and 84 ofthe locking cap 20 of the embodiment of FIGS. 1-6.

With continuing reference to FIG. 9, the bottom surface 166 of theflanged portion 164 of locking cap 120 is configured in substantiallythe same manner as the bottom surface 66 of locking cap 20 in that it isprovided with an elongate recess 168 for accommodating a spinal rod whenthe locking cap 120 is in an unlocked position, first and secondbifurcated transverse recesses 172 and 174 which intersect the elongaterecess 168 at opposite 45° angles to accommodate the spinal rod when thelocking cap 120 is in either of two intermediate positions, and abifurcated orthogonal recess 170 which intersects the elongate recess ata 90° angle to accommodate the spinal rod when the locking cap 120 is ina final locked position, as shown in FIG. 10. It will be readilyappreciated that locking cap 120 is engaged with fastening device 110 ina manner that is substantially similar to the manner in which lockingcap 20 is engaged with bone fastener 14 and hook 16, and that theconfiguration of the bottom surface of flanged portion 164 provides thesame benefits afforded by the flanged portion 64 of locking cap 20.

Referring now to FIG. 11, there is illustrated two additional fasteningdevices constructed in accordance with the subject disclosure in theform of a multi-axial bone screw 214 and a right-angle hook 216 whichare provided for securing spinal rod 212 to the spine during a spinalstabilization procedure. Both fastening devices employ a novel toploaded two-piece locking cap, designated generally by reference numeral220, which will be described in greater detail hereinbelow withreference to FIGS. 12 and 13. The novel two-piece locking cap achievessignificant clinical advantages over the prior art through itsreliability and the ease in which it is installed during a spinalstabilization procedure. As with respect to the previously describedembodiments of FIG. 1, the novel two-piece locking cap may be used inconjunction with other types of fasteners commonly employed in spinalstabilization procedures. Moreover, while the two-piece locking capillustrated in FIG. 11 is employed with a multi-axial bone screw, it isreadily apparent that the same two-piece locking cap could be employedwith a fixed axis bone screw such as that which is illustrated in FIG.1.

Referring to FIGS. 12A and 13, the multi-axial bone screw 214 includes ahead portion 222 defining a horizontal axis “x” and a vertical axis “y”.A channel 228 extends through the head portion 222 along the horizontalaxis “x” for receiving an elongated spinal rod 212. Channel 228 isdefined by the interior surfaces of the side walls 230 and 232 of headportion 222. Bone screw 214 further includes a fastener portion 224,which includes a generally spherical head 225 and a threaded body 226.Threaded body 226 depends from and is monolithically formed with thespherical head 225. The threaded body includes a helical threadformation that is particularly adapted to securely engage the vertebralbodies of the spine.

The head portion 222 of multi-axial bone screw 214 further defines agenerally cylindrical vertical channel 227, which extends through and isaligned with the vertical axis “y” of the head portion 222. Verticalchannel 227 is configured to receive and accommodate the fastenerportion 224 of bone screw 214. More particularly, as best seen in FIG.13, a lower interior surface portion of vertical channel 227 defines anannular seating surface 229 configured to cooperate with the lowerhemi-spherical region of spherical head 225. The cooperative engagementbetween the two structures permits the relative movement of the fastenerportion 224 with respect to the head potion 222 about the vertical axisy. The multi-axial motion afforded thereto, enhances the operationalrange of bone screw 214, providing greater flexibility to the surgeonduring a spinal stabilization procedure.

Bone screw 214 further includes an annular retention ring 232 that isaccommodated within a corresponding annular groove 234 formed within thecylindrical wall of vertical channel 227 (see FIG. 13). Retention ring232 is adapted to positively engage the spherical head 225 and aiding inits stabilization. In addition, as best seen in FIG. 13, the lowerhemi-spherical region of head 225 is scored with a series of circularridges adapted to enhance the frictional coefficient of the seatingsurface defined thereby.

Referring to FIG. 12A, bone screw 214 further includes a two-piecelocking cap 220 which is dimensioned and configured for reception andengagement in the horizontal channel 228 of head portion 220 to securethe position of head portion 222 with respect to spinal rod 212 during aspinal stabilization procedure. In addition, as described in detailhereinbelow with respect to FIG. 13, the securement of locking cap 220within channel 228 also achieves positive fixation of the angularposition of the fastener portion 224 with respect to the head portion222 and the vertical axis “y” defined thereby.

As illustrated in FIGS. 12A and 12B, locking cap 220 includes an upperportion 220 a and a lower portion 220 b. The upper portion 220 aincludes a cylindrical cap body 280 defining an axial reception port 282for receiving a tool or working implement that applies torque to the capduring installation. Upper portion 220 a further includes a pair ofcircumferentially opposed arcuate engagement flanges, 284 and 286 whichextend radially outwardly from cap body 280. Engagement flanges 284 and286 include inclined radially inwardly slopping camming surfaces forcooperating with complementary opposed arcuate engagement slots 294 and296 formed in the opposed side walls 230 and 232 of head portion 222(see FIG. 13). As described in more detail hereinbelow with respect toFIGS. 14 a-14 d, the flanges 284, 286 become engaged in correspondingslots 294, 296 upon rotation of the upper portion 220 a of locking cap220 relative to the head portion 222 of bone screw 214.

The lower portion 220 b of locking cap 220 is configured for cooperativereception within the cylindrical vertical channel 227 of head portion222 and is adapted to engage the spinal rod 212 extending through thehorizontal channel 228 of head portion 222. More particularly, the body285 of the lower portion 220 b has curved exterior surfaces, whichcomplement the curvature of the walls defining vertical channel 227.Thus, when the locking cap 220 is loaded into vertical channel 227, apositive mating relationship is achieved between the lower portion 220 bof locking cap 220 and vertical channel 227. As a result, the axialposition of lower portion 220 b becomes fixed with respect to headportion 222 and spinal rod 212. Furthermore, as best seen in FIG. 12B, ahemi-cylindrical channel 299 is formed in the undersurface of lowerportion 220 b for intimately cooperating with the cylindrical spinal rod212 upon loading the locking cap 220 in vertical channel 227. Bodyportion 285 includes an extension flange 302 which aides in thealignment and positioning of the lower cap portion 220 a with respect tospinal rod 212.

As best seen in FIG. 12B, the bottom surface of the upper portion 220 aof locking cap 220 includes a recessed seating area 287 and anassociated axial reception bore 288. The recessed seating area 287 isdimensioned and configured to accommodate the body of the lower portion220 b of locking cap 220, while the reception bore 288 is dimensionedand configured to receive and engage an axial post 298 which projectsfrom the upper surface 295 of the lower portion 220 b of locking cap220. More particularly, during assembly, when the axial post 298 isreceived by the reception bore 288, the top end of the post is swaged(flared out) to join the two components together (see FIG. 13). Theinteraction of the axial post 298 and axial reception bore 288facilitates relative rotational movement of the upper portion 220 arelative to the lower portion 220 b when the locking cap 220 is loadedinto and locked in the head portion 222 of bone screw 214 during aspinal stabilization procedure.

As described in detail hereinbelow with reference to FIGS. 14A-14C, thetwo-part locking cap enables a surgeon to load the locking cap 220 intovertical channel 227 and properly position the lower portion 220 bagainst the spinal rod 212 so as to ensure an intimate engagementbetween the hemi-cylindrical channel 299 and the cylindrical surface ofthe spinal rod. Thereafter, the upper portion 220 a may be rotated intoa locked portion relative to the lower portion 220 b.

Referring now in detail to FIGS. 14A-14C, during a spinal stabilizationprocedure, the fastener portion 226 of bone screw 214 is first seatedwithin the head portion 222. Then, the head portion 222 is positioned atthe surgical site in such a manner so that the elongated spinal rod 212extends through the horizontal channel 228 as illustrated in FIG. 14A.Thereafter, if necessary, the fastener portion 226 may be moved into adesired angular orientation by the surgeon and subsequently mounted tothe spinous process using suitable surgical instruments.

With reference to FIG. 14B, once the appropriate position of thefastener portion 226 has been established by the surgeon, the lockingcap 220 is loaded into the vertical channel 227 of head portion 222along the vertical axis “y” defined thereby. At such a time, thehemi-cylindrical channel 299 on the undersurface of lower portion 220 bwill become intimately engaged with the cylindrical surface of thespinal rod 212 and it will be maintained in a fixed axial orientationwith respect to the spinal rod due to the mating relationship betweenthe body of the lower portion 220 b and the vertical channel 227.

Locking cap 220 must be loaded in such a manner so that the radiallyoutwardly extending engagement flanges 284 and 286 of upper portion 220a are parallel to the axis of the spinal rod 212, as illustrated in FIG.14B. Otherwise, the flanges will interfere with the opposed side walls230 and 232 of the head portion 222. Furthermore, care must be taken toensure that the upper portion 220 a of locking cap 220 is positioned insuch a manner so that the low sides of the flanges (e.g. 284 a) arealigned with the high sides of the engagement channels (e.g. 294 a), orthe flanges will not cammingly engage the channels upon rotation of theupper portion 220 a of the locking cap 220 relative to the head portion222 of bone screw 214.

Once the upper portion 220 a of locking cap 220 has been properlyoriented with respect to head portion 222 with the extension flange 302in alignment with spinal rod 212, it is rotated in a clockwise directionabout the vertical axis “y” relative to the lower portion 220 b oflocking cap 220 and the head portion 222 of bone screw 214 using anappropriate surgical implement or tool (not shown). Thereupon, thearcuate engagement flanges 284, 286 of upper portion 220 camminglyengage the corresponding engagement slots 284. Once rotated into alocked portion, the lower portion 220 b of the locking cap 220 will beseated within the recessed seating area 287 defined in the bottomsurface 285 of the upper portion 220 a of locking cap 220 (See FIG. 13).At such a time, the position of the head portion 222 of bone screw 214is fixed with respect to longitudinal axis of spinal rod 212 and theposition of the fastener portion 226 of bone screw 214 is fixed withrespect to the vertical axis “y” defined by head portion 222 of bonescrew 214, as illustrated in FIG. 14C.

Referring now to FIGS. 15 and 16, the right-angle hook 216 of thesubject disclosure includes a head portion 242 defining a horizontalaxis x and a vertical axis “y”. A hook portion 246 depends from the headportion 242 to facilitate securement of the device to a vertebral bodyof the spine. A channel 248 extends through the head portion 242 alongthe horizontal axis thereof for receiving elongated spinal rod 212.Channel 248 is defined by the interior surfaces of opposed upstandingside walls 250 and 252 and a contoured lower surface extendingtherebetween for complementing the shape of the rod. Channel 248 isfurther configured to receive a two-piece locking cap 220 adapted tosecure the position of hook 216 with respect to spinal rod 212 during aspinal stabilization procedure.

As discussed hereinabove with respect to multi-axial bone screw 214, thelocking cap 220 includes an upper portion 220 a and a lower portion 220b, which are rotatably joined together. The upper portion includes apair of circumferentially opposed arcuate engagement flanges 284 and 286for cooperating with complementary opposed arcuate engagement slots 255and 257 formed in the opposed side walls 250 and 252 of head portion242. As described in more hereinabove with respect-to FIGS. 14A-14C, theflanges 284, 286 become engaged in corresponding slots 255, 257 uponrotation of the upper portion 220 a of locking cap 220 relative to thelower portion 220 b of the locking cap and the head portion 242 ofright-angle hook 216.

Although the apparatus disclosed herein has been described with respectto preferred embodiments, it is apparent that modifications and changescan be made thereto without departing from the spirit and scope of theinvention as defined by the claims.

1. A method of securing a spinal rod to a spine comprising: providing ahead portion having a channel extending therethrough for receiving aspinal rod, the channel in the head portion being bounded by a firstside wall having a first slot and a second side wall having a secondslot; providing a bone fastener depending from the head portion;arranging the spinal rod in the channel of the head portion; providing alocking cap having first and second portions that are rotatable relativeto one another, the first portion of the locking cap havingdiametrically opposed first and second flanges that are spaced from oneanother and the second portion of the locking cap having an undersidewith a recess; assembling the locking cap with the head portion so thatthe recess of the second portion of the locking cap is in contact withthe spinal rod and so that the opposed first and second flanges of thefirst portion of the locking cap are aligned with the channel extendingthrough the head portion; while maintaining the recess of the secondportion of the locking cap in contact with the spinal rod, rotating thefirst portion of the locking cap so that the first flange engages thefirst slot in the first side wall of the head portion and the secondflange engages the second slot in the second side wall of the headportion.
 2. The method as claimed in claim 1, wherein rotation of thefirst portion of the locking cap is translated into a locking forceapplied by the second portion of the locking cap onto the spinal rod. 3.The method as claimed in claim 1, wherein the locking cap is a two-partlocking cap consisting of the first portion and the second portion. 4.The method as claimed in claim 1, wherein the rotating step comprisesrotating the first portion of the locking cap about ¼ turn.
 5. Themethod as claimed in claim 1, wherein the bone fastener is a bone screwor a bone hook.
 6. The method as claimed in claim 1, wherein the firstand second flanges extend only partially around the first portion of thelocking cap.
 7. The method as claimed in claim 1, wherein the bonefastener is pivotable relative to the head portion before the rotatingthe first portion of the locking cap step.
 8. The method as claimed inclaim 1, wherein the first portion of the locking cap is mechanicallycoupled with the second portion of the locking cap so that the first andsecond portions are rotatable relative to one another.
 9. The method asclaimed in claim 1, wherein the spinal rod has a cylindrical shape andthe recess at the underside of the second portion of the locking cap hada cylindrical surface that conforms to the cylindrical shape of thespinal rod.
 10. The method as claimed in claim 1, wherein thediametrically opposed first and second flanges have an arcuate shape andthe first and second slots in the head portion have an arcuate shape.11. A method of securing a spinal rod to a spine comprising: providing ahead portion having a channel extending therethrough for receiving aspinal rod, the channel in the head portion being bounded by a firstside wall and a second side wall; providing a bone fastener dependingfrom the head portion; arranging the spinal rod in the channel of thehead portion; providing a locking cap having first and second portionsthat are rotatable relative to one another, the second portion of thelocking cap having an underside with a recess; assembling the lockingcap with the head portion so that the first portion is between the firstand second side walls and so that the recess of the second portion ofthe locking cap is in contact with the spinal rod; while maintaining therecess of the second portion of the locking cap in contact with thespinal rod, rotating the first portion of the locking cap, such rotationtranslating into a locking force applied by the second portion of thelocking cap onto the spinal rod.
 12. The method as claimed in claim 11,wherein the locking cap is a two-part locking cap consisting of thefirst portion and the second portion.
 13. The method as claimed in claim11, wherein the first side wall has a first slot, the second side wallhas a second slot, and the first portion of the locking cap hasdiametrically opposed first and second flanges that are spaced from oneanother.
 14. The method as claimed in claim 13, further comprising:before the rotating step, aligning the opposed first and second flangesof the first portion of the locking cap with the channel; and during therotating step, engaging the first flange with the first slot of the headportion and the second flange with the second slot of the head portion.15. The method as claimed in claim 11, wherein the rotating stepcomprises rotating the first portion of the locking cap about ¼ turn.16. The method as claimed in claim 11, wherein the bone fastener is abone screw or a bone hook.
 17. The method as claimed in claim 13,wherein the first and second flanges extend only partially around thefirst portion of the locking cap.
 18. The method as claimed in claim 11,wherein the bone fastener is pivotable relative to the head portionbefore the rotating the first portion of the locking cap step.
 19. Themethod as claimed in claim 11, wherein the first portion of the lockingcap is mechanically coupled with the second portion of the locking capso that the first and second portions are rotatable relative to oneanother.
 20. The method as claimed in claim 11, wherein the spinal rodhas a cylindrical shape and the recess at the underside of the secondportion of the locking cap had a cylindrical surface that conforms tothe cylindrical shape of the spinal rod.
 21. The method as claimed inclaim 13, wherein the diametrically opposed first and second flangeshave an arcuate shape.
 22. The method as claimed in claim 13, whereinthe first and second slots in the head portion have an arcuate shape.23. A method of securing a spinal rod to a spine comprising: providing ahead portion having a channel extending therethrough for receiving aspinal rod, the channel in the head portion being bounded by a firstside wall having a first slot and a second side wall having a secondslot; providing a bone fastener depending from the head portion, thebone fastener being pivotable relative to the head portion; seating thespinal rod in the channel of the head portion; providing a locking caphaving first and second portions that are rotatable relative to oneanother, the first portion of the locking cap having diametricallyopposed first and second flanges that are spaced from one another andthe second portion of the locking cap having an underside with a recess;assembling the locking cap with the head portion so that the recess ofthe second portion of the locking cap is in contact with the spinal rodand so that the opposed first and second flanges of the first portion ofthe locking cap are aligned with the channel extending through the headportion; rotating the first portion of the locking cap so that the firstflange engages the first slot in the first side wall of the head portionand the second flange engages the second slot in the second side wall ofthe head portion.
 24. The method as claimed in claim 23, wherein therotating step comprises rotating the first portion of the locking capabout ¼ turn.
 25. The method as claimed in claim 23, wherein the bonefastener is a bone screw or a bone hook.
 26. The method as claimed inclaim 23, wherein the first and second flanges extend only partiallyaround the first portion of the locking cap.
 27. The method as claimedin claim 23, wherein the bone fastener is pivotable relative to the headportion before the rotating the first portion of the locking cap step.28. The method as claimed in claim 23, wherein the first portion of thelocking cap is mechanically coupled with the second portion of thelocking cap so that the first and second portions are rotatable relativeto one another.
 29. The method as claimed in claim 23, wherein thespinal rod has a cylindrical shape and the recess at the underside ofthe second portion of the locking cap had a cylindrical surface thatconforms to the cylindrical shape of the spinal rod.
 30. The method asclaimed in claim 23, wherein the diametrically opposed first and secondflanges have an arcuate shape.
 31. The method as claimed in claim 23,wherein the first and second slots in the head portion have an arcuateshape.
 32. A method of securing a spinal rod to a spine comprising:providing a head portion having a channel extending therethrough forreceiving the spinal rod, the channel in the head portion being boundedby a first side wall having a first slot and a second side wall having asecond slot; providing a bone fastener depending from the head portion;arranging a spinal rod having a longitudinal axis in the channel of thehead portion; providing a locking cap having first and second portionsthat are rotatable relative to one another, the first portion of thelocking cap having diametrically opposed first and second flanges thatare spaced from one another and the second portion of the locking caphaving an underside with a recess; assembling the locking cap with thehead portion so that the recess of the second portion of the locking capis in contact with the spinal rod and so that the opposed first andsecond flanges of the locking cap are at least partially aligned withthe longitudinal axis of the spinal rod; rotating the first portion ofthe locking cap so that the first flange is disposed in the first slotin the first side wall and the second flange is disposed in the secondslot in the second side wall and so that the opposed flanges extendalong an axis that traverses the longitudinal axis of the spinal rod.33. The method as claimed in claim 32, wherein the rotating stepincludes rotating the first portion of the locking cap about ¼ turn. 34.The method as claimed in claim 33, wherein each of the slots has aterminal end that stops the first portion of the locking cap fromfurther rotation beyond the about ¼ turn.
 35. The method as claimed inclaim 33, wherein the first and second flanges are arcuate flanges andthe first and second slots are arcuate slots.
 36. The method as claimedin claim 35, wherein the arcuate flanges have curved surfaces thatconform to the shape of the arcuate slots.
 37. The method as claimed inclaim 32, wherein the first portion of the locking cap has an outerperimeter and the first and second flanges extend only partially aroundthe outer perimeter.
 38. A method of securing a spinal rod to a spinecomprising: providing a spinal rod having a longitudinal axis and acylindrical exterior surface; providing a head portion having a channelextending therethrough for receiving the spinal rod, the channel in thehead portion being bounded by a first side wall having a first slot anda second side wall having a second slot, the head portion defining acentral axis perpendicular to the channel, an aperture at a lower end ofthe head portion and a seat surrounding the aperture at the lower end ofthe head portion; providing a fastener including a fastener head and athreaded body depending from the fastener head and assembling thefastener with the head portion so that the fastener head is in contactwith the seat of the head portion and the threaded body extends throughthe aperture at the lower end of the head portion; arranging the spinalrod in the channel of the head portion so that the longitudinal axis ofthe spinal rod extends between the first and second side walls of thehead portion; providing a locking cap having a first portion and asecond portion that are rotatable relative to one another, the firstportion of the locking cap having diametrically opposed flanges that arespaced from one another, the second portion of the locking cap having anunderside with a recess having a cylindrical surface that conforms tothe cylindrical exterior surface of the spinal rod; assembling thelocking cap with the head portion so that the recess of the secondportion of the locking cap is in contact with the exterior surface ofthe spinal rod and so that the diametrically opposed flanges extend awayfrom one another along a first axis that is substantially parallel tothe longitudinal axis of the spinal rod; after the assembling step,rotating the first portion of the locking cap about ¼ turn so that eachof the diametrically opposed flanges engage one of the first and secondside walls and so that the diametrically opposed flanges extend awayfrom one another along a second axis that traverses the longitudinalaxis of the spinal rod.
 39. The method as claimed in claim 38, whereinthe first and second portions of the locking cap rotate relative to oneanother during the rotating the first portion of the locking cap about ¼turn step.
 40. The method as claimed in claim 38, wherein the fastenerhead has an underside having a curved surface.
 41. The method as claimedin claim 38, wherein the first and second flanges are arcuate flangesand the first and second slots are arcuate slots.
 42. The method asclaimed in claim 38, wherein the fastener is pivotable relative to thehead portion before the rotating the first portion of the locking capstep.
 43. The method as claimed in claim 38, wherein the locking cap hasa bore at a top surface thereof adapted to receive a driving tool. 44.The method as claimed in claim 38, wherein the second portion of thelocking cap has a convex curved outer surface that conforms to curvedinner surfaces of the first and second side walls of the head portion.45. The method as claimed in claim 38, wherein the opposed flangesextend only partially around a perimeter of the first portion of thelocking cap.